1. Field of The Invention
The present invention relates to a jack, and more particularly to a electrically operated screw-type jack. The present invention is an improvement made over the conventional hand-operated or electrically operated jacks used in working on vehicles.
2. Description of Prior Art
Conventional hand-operated jacks used in working on vehicles are operated by hands of a person. Since the person must stand near the load to be lifted while operating the jack, the jack can be unsafe. Furthermore, conventional jacks require too much time to lift the lifting ram. Since great power is required to operate conventional jacks, such jacks are not easily used by females or weak persons.
Therefore, there have been many attempts to solve the problems of the hitherto used hand-operated jacks. For example, U.S. Pat. No. 4,609,197 entitled "SCREW JACK" reveals an electrically operated screw-type jack as shown in accompanying drawing, FIG. 6.
As indicated in FIG. 6, the conventional electric screw-type jack generally consists of a jack body (a), a servo motor (b) mounted beside the jack body (a), a driving worm (c) and a worm wheel (d) interlocked with each other by the servo motor (b), and a lifting ram (f), being provided with a spur gear (e) fixedly mounted at the lowermost end thereof, which can move upward or downward depending on rotating directions of the servo motor (b). However, in the conventional electric screw-type jack, the power from the servo motor (b) is directly transmitted to the worm wheel (d) and the spur gear (e) without any addition of speed-reduction mechanism, so that the power transmitting parts, such as the driving worm (c), the worm wheel (d) and the spur gear (e) raise the contact resistance therebetween during the lifting of vehicles of relatively heavy weight. Therefore, the conventional electrically operated screw-type jack have some problems because of the repeated abrasion of the power transmitting parts, and more particularly when lifting heavy-industrial vehicles such as a dump truck and the like. There may be failures of the servo motor and the power transmitting parts as a result of the deficient power of the servo motor.